1. Field of the Invention
The present invention relates to the Multiprotocol Label Switching (MPLS) technology, and more particularly, to a method and devices for implementing group protection in an MPLS network.
2. Background of the Invention
The Label Switched Path (LSP) unidirectional protection technique is a mature protection technique in MPLS networks, and includes such types of protection as 1+1 type, 1:1 shared mesh type and packet 1+1 type. All of these types are trail-based protection types.
Along with the continuous development of the protection switching of MPLS networks, an LSP bidirectional protection switching, an Automatic Protection Switching (APS) protocol and an MPLS SubNetwork Connection Protection (SNCP) technique are further provided based on the existing trail-based LSP unidirectional protection switching. The MPLS SNCP includes the SNCP with Sublayer monitoring (SNC/S) technique, the Non-intrusively monitored SNCP (SNC/N) technique and the Inherently monitored SNCP (SNC/I) technique. The MPLS SNCP technique protects some parts of the LSP, and is applicable to segment-protection of inter-domain LSPs. A working LSP may be a part of an LSP connection in a sub-network, or may be the whole LSP connection in a sub-network.
The SNC/S divides the LSP into multiple nested sublayers, and there is independent MPLS Operation and Maintenance (OAM) information in each sublayer to monitor survivability of the LSP in the sublayer. The state of a sublayer LSP is monitored by the MPLS OAM, and APS information is transmitted in the SNC. The SNC/S can be used in a bidirectional/unidirectional 1+1 protection or a bidirectional/unidirectional 1:1 protection.
The SNC/N is applicable to protection switching based on Non-intrusively monitoring in the LSP sub-network. The SNC/N may include two modes: an end-to-end mode and a sublayer mode. The former serves for protection switching of end-to-end LSP in the LSP sub-network, and the latter serves for protection switching of segment LSP in the sub-network. The SNC/N is preferably used in a unidirectional 1+1 protection and needs no transmission of APS protocol information.
The SNC/I technique is applicable to applications in which the MPLS functions as a client and performs protection switching based on trail monitoring information of a server layer. In this case, a Server/MPLS adaptation layer transmits a Server Signal Degrade (SSD)/Server Signal Fail (SSF) of the server layer to the MPLS layer as a triggering signal of the LSP protection switching, and the APS is transmitted in the SNC. The SNC/I can be used in a bidirectional/unidirectional 1+1 protection or in a bidirectional/unidirectional 1:1 protection.
The LSP protection may include trail-based protection and SubNetwork Connection (SNC) protection according to protection objects. The trail-based protections may further include individual trail protections and group trail protections, the SNC protection may further include individual SNC protection and group SNC protection.
When using the trail-based LSP group protection technique in existing MPLS networks to implement the trail-based LSP group protection, operations shown in FIG. 1 may be performed. As shown in FIG. 1, when working traffic is from Network Element (NE) A to NE Z, NE A is the source and NE Z is the sink; when the working traffic is from NE Z to NE A, NE Z is the source and NE A is the sink. NE A and NE Z have selectors and bridges respectively. The bridge of the source bridges the working traffic to the working LSP (1:1 type), or to the working LSP and the protection LSP (1+1 type), and the selector of the sink receives the working traffic from the working LSP. The implementation of group protection may include following processes. All of the working LSPs are merged into one merged LSP and the protection LSPs are merged into one merged LSP. When a failure, such as, a Signal Degrade (SD) or a Signal Fail (SF), is detected on the merged LSP of the working LSPs while no SD/SF occurs on the merged LSP of protection LSPs, the LSP group protection will be triggered to switch the working traffic to the protection ISP. In the 1:1 protection, the bridge of the source switches the working traffic on the working LSP to the protection LSP, and the selector of the sink receives the working traffic from the protection LSP. In the 1+1 protection, since the working traffic is already on the protection LSP, the source needs no operations and the selector of the sink selects receiving the working traffic from the protection LSP.
In the LSP protection techniques in existing MPLS sub-networks, when LSP group protection is needed in the SNC, the LSP group protection may be realized using the SNC/N or the SNC/S technique. FIG. 2 shows a schematic diagram illustrating the operations of group protection using the SNC/S technique, and the operations of the group protection using the SNC/N technique are similar. As shown in FIG. 2, the implementation of the group protection may include following processes. All of the working LSPs are merged into one merged LSP sub-trail and the protection LSPs are merged into one merged LSP sub-trail, and the merged LSP sub-trail may be monitored through the SNC/N or the SNC/S principle. When the SD or the SF occurs on the merged LSP sub-trail of the working LSPs while no SD/SF occurs on the merged LSP sub-trail of protection LSPs, the LSP group protection will be triggered.
As described above, either for the trail-based LSP group protection or for the SNC/N or SNC/S-based LSP group protection, the solution above needs to merge trail-based working/protection LSPs or SNC-based working/protection LSPs into a merged LSP trail or a sub-trail, and to implement the trail-based LSP group protection or the LSP group protection in MPLS sub-network, by monitoring the merged LSP trail or the sub-trail. Therefore, the technical solution of implementing the group protection in MPLS networks is complicated. Furthermore, in a protection switching, all merged LSPs trail needs to be switched simultaneity, which makes it hard to meet the requirements of flexible protection switching in the protection switching, such as the requirement of protection switching for partial paths.